His name was Nicholas Clarke but friends called him Ratty, and the only good thing to be said about the way he died was that he probably knew nothing about it. A shot rang out in the distance. It hit him in the head.

The betting is that Ratty, 19, wasn't even the intended target. There probably was no specific target that day on the Myatts Field estate in Brixton, south London. Just boys and men with guns and no real understanding of the fragility of life.

There are photographs stuck to the lamppost where he fell and they show Ratty as a handsome dude. Wide eyes; short hair; clear brown skin. He had plans, his aunt and uncles tell me. To be a vet perhaps. Maybe a model. Plans and friends, and he was with his friends when the gunman struck. But that was two years ago and everyone is keeping their secrets. There's a <a href="http://cms.met.police.uk/news/appeals/anniversary_appeal_after_murder_of_student_in_brixton" title="reward for <00ad>convicting his killer">reward for convicting his killer: £20,000, so far unclaimed.

So here we are in Brixton, in the middle of Myatts Field, on the second anniversary of Ratty's death. The initial investigation has gone cold, so everyone is using the anniversary to try again; to raise a flag, jog memories. In military terms, we'd call it a surge.

The flurry begins. In the foreground, officers in overcoats distributing flyers. In the distance, Ratty's uncles and aunt; anxious, strained, talking to a student television crew.

It was about turf, one officer tells me. And it was routine, says the Rev Ivelaw Bowman, an advisor to Trident, Scotland Yard's gun crimes unit, emerging from its new community engagement van in a thick blue fleece. How many of these have you seen, I ask him. "Too many," he says quickly. "What really brings it home is when you accompany the mothers to the mortuary and they see the body for the first time. They collapse into a heap."

There were fewer of these murders last year than the year before, but gun crimes are up 11% in the capital and thus no one is surprised as they are reminded about what happened to Ratty. Someone knows something. The police are sure of it; but getting to the truth is always difficult. Sometimes it's about forensics and clever deduction. But sometimes it's just consciences and a leap of faith.